1. Field of the Invention
The present invention relates to a CD-ROM drive, and more particularly, to a method for adjusting the reproduction speed of a CD-ROM drive according to variations of a supply voltage, and a device suitable for the method.
2. Description of the Related Arts
In a CD-ROM drive in a computer system, data cannot be read out properly if a supply voltage supplied varies significantly, especially when the supply voltage drops below a reference voltage, for example, in a notebook computer which uses only a battery. Thus, a system error may occur, which should be prevented by adjusting the speed of the CD-ROM drive.
FIG. 1 is a block diagram of a conventional CD-ROM drive.
In FIG. 1, a servo 120 controls the speed of a spindle motor 110. The spindle motor 110 rotates the turntable 100 on which a CD-ROM is placed. A preamplifier 130 amplifies signal read out from the disk by use of an optical pickup (not shown) to a predetermined level. An interface 140 transmits and receives data to and from a host computer (not shown). A digital signal processor (DSP) 150 controls the servo 120, analog-to-digital converts the amplified signal output by the preamplifier 130, and demodulates and error-correction-decodes such data. When the servo 120 is locked, the DSP 150 outputs the error-corrected data to the interface 140. A microcontroller 160 determines whether the servo 120 is normally controlled by the DSP 150 so that the servo 120 is normally operated.
Here, if the servo 120 is not normally operated, the microcontroller 150 retries several times such that the servo 120 is normally controlled. If the servo 120 is not normally operated despite the retrials, the microcontroller 160 stops the CD-ROM drive and sends an error signal to the host computer via the interface 140.
In the conventional CD-ROM drive, in case that a supply voltage drops, the error correcting capability of the DSP is reduced, and the torque of the spindle motor is lowered so that an intended rotating speed cannot be achieved. As a result, the DSP 130 cannot normally correct an error in the data and the servo 120 cannot be unlocked. Therefore, the system cannot operate properly. Such a problem becomes serious especially when a system is driven with only a battery without another power source, e.g., in a multimedia notebook computer.